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Gas Chromatography.
Electron Capture Detector.
Gas chromatography
Information about gas chromatography in general can be found in the application sheet “Gas
Chromatography” (GC).
Environmental measurements of deposits, water and air are becoming more and more important in all
parts of the world. One group of environmental threats are polyhalogenated organic compounds such as
polychlorinated biphenyls (PCB’s), pesticides and other halogenated organics. Even small concentrations
are causing damages and it is of great importance to be able to analyze those compounds correctly at low
concentrations (ppm and ppb). GC with Electron Capture Detector (ECD) is a very sensitive method and is well
suited for analysis of such polyhalogenated organic compounds.
Analyze with the GC-ECD
In the electron capture detector a beta emitter such as radioactive tritium or 63Ni is used to ionize the carrier
gas. Fast beta particles generated by the radioactive source collide with the molecules of the carrier or
make-up gas. By impact ionization,, free slow-moving electrons are produced which generate a measurable
and steady current. If the GC effl uent contains organic molecules with electronegative functional groups,
such as halogens, phosphorous and nitro groups, electrons will be captured and the current will be reduced.
In comparison to a signal without sample compounds, the reduction in electron fl ow is proportional to the
quantity of electrophile sample components.
Gases
An important facet of GC-ECD is the carrier gas. The carrier gas transfers the sample from the injector, through
the column and into the EC-detector. As for all GC techniques the carrier gas must be inert and may not be
adsorbed by the column material. Because the ECD is sensitive to water, the carrier gas must be dry. Besides,
the halocarbon content must be as small as possible, since these are the typical compounds to be analyzed
with the ECD. Halocarbon-free helium or nitrogen are therefore recommended as carrier gases for GC-ECD.
To generate free slow-moving electrons the ECD requires nitrogen or methane, where methane is used in a
form of a methane/argon mixture. Both nitrogen and the methane mixture are used as detector gases as well
as carrier gases.
Like all chromatographic analytical processes, gas chromatography is a relative method, i.e. calibration with
a standard mixture is required. In a fi rst analysis a certifi ed standard mixture is measured. By comparable
measurements, the sample components can be identifi ed and their proportion, and thereby their
concentration, determined.
The selection of gases, fi ttings and pipes as well as the installation is crucial to preserve the sensitivity,
detection limits and reproducibility of a detector. Particular attention should be given to the choices.
Gas outlet
Signal
Cathode
Anode
63
Ni plated
surface
Detector gas
Gas inlet
from column
HiQ® product program
The HiQ® product program offers a wide range of gas qualities and equipment that fulfi ll the demands
concerning analytical techniques of AAS.
Carrier and detector gases
Carrier gas
Specifications
Detector gas
10% n.a. n.a.
Calibration mixtures
Recommended central
gas supply
Recommended cylinder
regulators
To obtain optimal analytical results, AGA recommends the following gas qualities for GC-ECD analysis:
Halocarbon free helium 5.0 or product code 6008
Halocarbon free nitrogen 5.5 product code 6014
O2
N2
Halocarbons as SF6
CnHm
H2O
Product code
Halocarbon free
helium He 5.0
≤ 2 ppm
≤ 5 ppm
≤ 1 ppb
≤ 1 ppm
≤ 3 ppm
6008
Halocarbon free nitrogen 5.5 product code 6014
or
Halocarbon free
methane instarg 5%
Component concentration
5% CH4
Balance gas
Argon
Halocarbons as SF6
≤ 1 ppb
Product code
6172
Halocarbon free
nitrogen N2 5.5
≤ 5 ppm
≤ 5 ppm
≤ 5 ppm
≤ 5 ppm
6014
Halocarbon free
methane instarg 10%
10% CH4
Argon
≤ 1 ppb
6173
For calibration mixtures please look into the HiQ® product catalog or ask your local sales representative.
HiQ® REDLINE central gas supply systems for inert and non-reactive gases. Group green for single gas supply
panels designed for pure gases and mixtures.
Group blue for single stage supply panels with internal purging designed for high purity gases and mixtures
including flammable gases.
HiQ® REDLINE single stage regulator, C200/1 for carrier and auxiliary gases. For calibration gases HiQ® REDLINE
two stage regulator, C200/2 provides a stable secondary outlet pressure. C200 regulators can be plain or equipped with a shut-off valve (type A) or a needle valve (type B).
For GC-ECD we recommend a C200 regulator in brass with a shut-off valve.
Outlet pressure
HiQ® REDLINE
bar psi
Product code
Single stage
C200/1 A, brass
0.2-3 3-45 3100
Single stage
C200/1 A, brass
0.5-6 8-85 5467
Two stage
C200/2 A, brass
0.2-3 3-45 5482
6
6
6
5%
5%
5%
5%
5%
5%
Please look into our HiQ® catalog ‘Biotech, Chemical, Petrochemical & Pharma-ceutical’, look into our web
site, http://hiq.aga.com, or contact your local AGA sales representative.
Blending tolerance
Analysis uncertainty
Shelf life
Sweden, AGA Gas AB, Phone +46 (0)8 706 95 00, Fax +46 (0)8 628 23 15, www.aga.se
Finland, Oy AGA Ab, Phone +358 (0) 10 2421, Fax +358 (0) 10 242 0311, www.aga.fi
Norway, AGA AS, Phone +47 23 17 72 00, Fax +47 22 02 78 04, www.aga.no
Denmark, AGA A/S, Phone +45 32 83 66 00, Fax +45 32 83 66 01, www.aga.dk
Iceland, ISAGA ehf., Phone +354 577 3000, Fax +354 577 3001, www.aga.is
Estonia, AS Eesti AGA, Phone +372 6504 500, Fax +372 6504 501, www.aga.ee
Latvia, AGA SIA, Phone +371 7023900, Fax +371 7023901, www.aga.lv
Lithuania, AGA UAB, Phone +370 5 2787788, Fax +370 5 2701191, www.aga.lt
® HiQ and HiQ REDLINE are registered trademark of the Linde Group.
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